The present invention relates to an electromagnetic reciprocating fluid apparatus, e.g. pumps and compressors, comprising a magnetic circuit device having induction coils and a pair of opposed magnetic poles, wherein magnetic force is intermittently induced between the magnetic poles by intermittently exciting the induction coils so that a magnetic armature is attracted and driven by the magnetic force to reciprocate a piston connected to the magnetic armature.
FIGS. 1 and 2 are schematic views of an electromagnetic reciprocating fluid apparatus used as a pump or a compressor.
As illustrated in the figures, the apparatus comprises an exciting circuit having induction coils 16 and 18 wound around magnetic pole members 10 and 12, respectively, and a half-wave rectifier 20. The apparatus further comprises a piston 24 slidably fitted in a cylinder 22. A magnetic armature 28 is secured to the rod portion of the piston 24. A coil spring 30 urges the piston 24 leftward as viewed in the figures.
When an AC voltage is applied to the exciting circuit, an electric current intermittently flows through the exciting circuit so that the induction coils 16 and 18 are intermittently excited to thereby intermittently induce magnetic force between the magnetic pole members 10 and 12. The magnetic armature 28 is therefore magnetically attracted rightward to drive the piston 24 rightward. When the magnetic force disappears, the piston 24 is driven leftward by the coil spring 30. In this way, the piston 24 is reciprocated. The cylinder 22 is provided with a pair of check valves 32 and 34. The reciprocating motion of the piston 24 causes the check valves 32 and 34 to open and close alternately, thereby allowing a fluid to flow in through a fluid inlet 38 formed in a housing 36 and to flow out through a fluid outlet 40 formed in the housing 36.
FIGS. 3 and 4 show an example of a specific arrangement of the electromagnetic reciprocating fluid apparatus.
The apparatus comprises magnetic pole members 10 and 12, induction coils 16 and 18, a cylinder 22, a piston 24, a magnetic armature 28, a coil spring 30, check valves 32 and 34, and a housing 36 having a fluid inlet 38 and a fluid outlet 40 in the same way as the apparatus shown in FIGS. I and 2. This type of electromagnetic reciprocating fluid apparatus is disclosed, for example, in Japanese Patent Publication No. Sho 57-30984.
FIG. 4 shows the relationship between the magnetic armature 28 and the magnetic pole members 10 and 12. More specifically, the magnetic pole members 10 and 12 are formed from mutually opposing portions projecting from the left and right side sections of a substantially quadrangular magnetic circuit member 41 made of a magnetic material and the induction coils 16 and 18 are respectively wound around the projecting portions. The magnetic pole members 10 and 12 have mutually opposing circular-arc surfaces 10′ and 12′ which are formed about an axis extending normal to the surface of FIG. 4 and through the center of the space between the magnetic pole members 10 and 12. The magnetic armature 28 extends along the axis and has a circular section.
In the apparatus having the above-described structure, the length of a stroke and the magnitude of a thrust of the piston 24 are determined as a function of the width and thickness or the cross sectional area of the magnetic pole members 10 and 12. In general, the width and thickness of the magnetic circuit member 41 are designed so that the magnetic flux density is substantially uniform throughout the magnetic circuit formed from the magnetic circuit member 41 and the magnetic pole members 10 and 12.
A computer simulation analysis of a magnetic circuit arranged as stated above reveals, however, that there are following problems:
In general, the magnetic circuit member 41 is designed to have the same thickness as that of the magnetic pole members 10 and 12, and the width of the magnetic circuit member 41 is determined according to the thickness. In the magnetic circuit thus arranged, at the comers of the magnetic circuit defined by the inner peripheral surface of the magnetic circuit member 41 and the outer peripheral surfaces of the pole members 10 and 12 intersecting the inner peripheral surface of the magnetic circuit member 41 there is caused concentration of lines of the magnetic force. The magnetic flux concentration increases the magnetic reluctance, causing degradation of the efficiency of the apparatus.